How T3/T4 regulated in the blood?
Hypothalamus secretes TRH which goes onto the the anterior pituitary gland through the pituitary portal vein. the pituitary gland secrete thyroid stimulating hormone. The thyroid stimulating hormone stimulates thyroid gland to secrete T3/T4
T3/T4 have inhibitory effect on hypothalamus and anterior pituitary
Levothyroxine - Drug that treats hypothyroidism. symptoms that may occur
- replace missing endogenous T3 and T4 with levothyroxine (T4)
- serum TSH should go down
- increases metabolic rate
- promotes growth and maturity
- Adverse effects: overexpression of T3 and T4. CNS excitability. Allergic skin reactions. Diarrhea, vomiting. Tachycardia, angina , cardiac arrest.
Thyroid gland produces and secretes two hormones:
T3 (tri-iodothyronine)
T4 (thyroxine)
Function of T3/T4
- regulate basal metabolic rate
- positive inotropic, chronotropic effects (make heart beat faster and contract harder)
- increase rate of metabolism of nutrients
- increase body temperature
- increase GI motility and appetite
- increase secretion of growth hormone
Primary hypothyroidism
dysfunction of the thyroid
Secondary hypothyroidism
due to the pathophysiology of the pituitary
Tertiary hypothyroidism
disorder of the hypothalamus
causes of hypothyroidism
- surgical removal of thyroid gland
- aggressive, or overtreatment of hyperthyroidism condition
- goiter often caused by insufficient iodine in developing countries
Symptoms of hypothyroidism
- constipation
- decreased metabolism/weight gain/appetite
- fatigue, muscle cramps, aches, weakness
- cold intolerance/decreased temp
- brittle/dry/hard nails
- restricted growth
- myxedema (peri-orbital edema, puffy dull face with dry skin)
- depression/irritability
Labs for hypothyroidism
- TSH will be high
- T3 and T4 will be low
- All newborns are tested at birth for thyroid function
- if untreated can lead to intellectual disabilities due to effects on brain development
Hyperthyroidism - types
high serum levels fo T3 and T4.
- Graves disease - autoimmune disorders in which antibody bind TSH receptor on thyroid
S&S of Hyperthyroidism
- diarrhea, nausea
- heat intolerance
- weight loss, increased metabolic rate
- increased heart rate
- insomnia
- Exophthalmos
- flushed
- palpitations
- increased appetite
- muscle weakness, heat intolerance, irritability, altered menstrual flow
Lab values hyperthyroidism
- TSH would be low
- T3 and T4 would be high
Two major treatments for hyperthyroidism
- radioactive iodine
- anti-thyroid drugs (Propylthiouracil) - used in hyperthyroisim caused by overproduction of thyroid hormone. establishes normal thyroid state prior to surgery or radioactive iodine treatment. inhibits synthesis of thyroid hormone. Suppresses peripheral conversion of T4 to T3 (because T3 is more potent)
